1. Field of the Invention
The present invention relates to a radio communication system and method and a mobile communication terminal device, and more particularly, relates to a code division multiple access (CDMA) cellular telephone system.
2. Description of the Related Art
Data transmissions using cellular telephone systems have been limited to computer communications executed by individual users using facsimile or modems, and there have been no information providing services for providing various information through a cellular network. This is partly because the cellular telephone system does not have a sufficient communication capacity. That is, all existing cellular telephone systems can do is to provide call services, and they do not have an extra communication capacity for providing other services.
In the United States, attempts are being made to standardize the CDMA cellular telephone system to initiate its services. The CDMA method has been used in new mobile communication systems such as personal communication service (PCS) systems, and it has been firmly believed that in the United States, this method will be most popular during the next generation.
The CDMA method is characterized by its communication capacity that is much larger than that of the conventional frequency division multiple access (FDMA) method. In the future, half or more of the 25 MHz frequency band assigned to existing cellular telephone systems and the 60 MHz frequency band assigned to the PCS system can be operated by the CDMA method to obtain a communication capacity about ten times as large as that of conventional methods. Thus, for CDMA cellular telephone systems, call services do not use up all the assigned frequency bands, and this system is expected to provide value-added services such as information provision.
The CDMA system has a large communication capacity, but its capacity is still smaller than that of cable communication networks. The communication capacity of the cable system can be increased easily by increasing the number of cables, whereas the code multiplexing capability and the number of frequency bands for the CDMA method are limited. Thus, the CDMA cellular telephone system must be efficient in providing services.
In addition, minimizing the charge for receiving services is important in spreading the services, so the amount of information that can be provided per frequency is desirably maximized to efficiently provide services.